58 lines
2.5 KiB
Python
58 lines
2.5 KiB
Python
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"""Daily filesystem capacity cache, persisted in RAM across monitor restarts."""
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import json
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import time
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from pathlib import Path
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from shutil import disk_usage
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class StorageCache:
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def __init__(self, path, reader=disk_usage, clock=time.time):
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self.path, self.reader, self.clock = Path(path), reader, clock
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self.values = None
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self.observed_at = None
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self.next_update_at = 0
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self.error = False
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try:
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data = json.loads(self.path.read_text())
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if not isinstance(data,dict):raise ValueError('invalid cache')
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retry = data.get('next_update_at')
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if data.get('error') is True and isinstance(retry,(int,float)) and self.clock() < retry <= self.clock()+3600:
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self.error, self.next_update_at = True, retry
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values = data['values']
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if all(isinstance(values[k], int) and not isinstance(values[k], bool) and values[k] >= 0 for k in ('total', 'used', 'free')) and values['total'] > 0 and values['used'] <= values['total']:
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at = data['observed_at']
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if isinstance(at, (int, float)) and 0 <= self.clock() - at < 90000:
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self.values, self.observed_at = values, at
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if not self.error:self.next_update_at = at + 86400
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except (OSError, ValueError, KeyError, TypeError):
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pass
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def sample(self):
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now = self.clock()
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if now < self.next_update_at:
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return self.values
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try:
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usage = self.reader('/')
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if usage.total <= 0 or not 0 <= usage.used <= usage.total or usage.free < 0:
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raise ValueError('invalid capacity')
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except (OSError, ValueError):
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self.error = True
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self.next_update_at = now + 3600
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self.persist()
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return self.values
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self.values = dict(total=usage.total, used=usage.used, free=usage.free)
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self.observed_at = now
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self.next_update_at = now + 86400
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self.error = False
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self.persist()
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return self.values
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def persist(self):
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try:
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self.path.parent.mkdir(parents=True, exist_ok=True)
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self.path.write_text(json.dumps(dict(values=self.values, observed_at=self.observed_at,
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next_update_at=self.next_update_at, error=self.error)))
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except OSError:
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# The in-memory sample remains valid even if the RAM cache cannot be persisted.
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pass
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